The Characteristics of Spontaneous Action Potential of Cardiac Myocytes in Rabbit Pulmonary Veins

Background and Objectives：Atrial fibrillation is one of the most prevalent arrhythmia with clinical signifi-cance. Recently, some subset of paroxysmal atrial fibrillation was reported to be originated from a focal, rapidly firing source inside the large thoracic veins, such as pulmonary veins, superior vena cava and coronary sinus. The pulmonary veins are known to be the most frequent source of this type of atrial fibrillation. The proximal segment of pulmonary vein was reported to be made up with cardiac muscle cells. This study was performed 1) to define the characteristics of action potential of cardiac myocytes inside the rabbit pulmonary vein in single cell preparation, 2) to observe the changes in action potential and current activation to acetylch-oline and isoproterenol, and 3) to compare these changes with those in atrial myocytes. Method and Results： In most of rabbit specimens, myocardial tissue extended over the pulmonary vein for a few millimeters (1-2.5 mm). Single atrial myocyte and myocyte in pulmonary vein were successfully isolated. With using whole cell patch clamp technique, spontaneous activities of action potentials (APs) with diastolic depolarization were observed in 75 % of pulmonary vein myocytes, in contrast to the absence of spontaneous activity in atrial myocytes. During spontaneous APs of pulmonary vein myocytes, the maximal diastolic potential was-50.5± 6.5 mV and peak potential was 32.5±9.5 mV, and the frequency of APs was 1-2.5 Hz. During perfusion o